One route to forming methyl mercaptan (MeSH) is through the reaction of methanol (MeOH) with hydrogen sulfide (H2S). This process is referred to herein as the “methanol route.” The general chemical reaction that is the basis of the methanol route is as follows: CH3OH+H2S→CH3SH+H2O. In industrial reactors, however, neither conversion of the reactants nor selectivity for methyl mercaptan is 100%. As used herein, the term “conversion” refers to the percentage of the initial amount of the substoichiometric reactant that is consumed in a reaction to produce methyl mercaptan and any secondary products. The part percentage of the consumed amount of the reactant which gives rise to methyl mercaptan alone is called “selectivity”. Accordingly, the yield of methyl mercaptan may be calculated as follows: yieldMeSH=(conversionReactant)(selectivityMeSH). In particular, side reactions of the methanol route often include formation of dimethyl ether (DME) and dimethyl sulfide (DMS). In a typical, non-recycle process, the methyl mercaptan would be separated from the by-products (e.g. dimethyl sulfide and dimethyl ether) and the by-products disposed of, resulting in a loss of carbon and sulfur. This loss translates to increased methanol and hydrogen sulfide raw material costs and lower overall methyl mercaptan yield.
Methods for recovering dimethyl sulfide from the product stream, mixing the recovered dimethyl sulfide with clean hydrogen sulfide, feeding the mixture to a catalytic reactor to convert part of the dimethyl sulfide to methyl mercaptan have been described in the art but have many disadvantages—e.g. cost, complexity, low yield. Accordingly, improved methods for producing methyl mercaptan are desired.